Re: Reducing the cost of garbage collecting small arrays

On 23/06/2011 09:54, Johan Tibell wrote:

On Thu, Jun 23, 2011 at 8:27 AM, Johan Tibell wrote:

...

...

Is 5 the optimal number of bits to slice off at a time (ie the best fanout)? It sounds like node copy cost on insert argues for a slightly narrower fanout. You'll be evacuating / scanning more words total, but new nodes may equate to less scanning overall (especially if this is running long enough to have some nodes get tenure).

I'm experimenting with this. 6 is far too much, making inserts 4-5x slower. 4 doesn't seem to improve things much (which is a bit counter-intuitive given that 6 made things so much work), but I need to experiment some more.

After some more testing I can improve the performance of insert by 30% by reducing the array size from 32 to 16. GC still dominates though.

I will try to look at this when I have some time. It could just be the cost of copying the extra data, though. This is probably another one of those cases where generational GC isn't helping, long-lived data is getting copied multiple times as it progresses from the young generation to the old. I want to look into some heuristics to try to detect when this is happening and vary the nursery size automatically. Cheers, Simon